This invention relates to the field of expandable intraluminal support devices such as stents and the like. Typically, stents are expandable, tubular metallic devices that are positioned within a patient's vasculature or other body lumen and expanded in order to support a vessel or body lumen at a desired intraluminal location to allow the flow of blood or other body fluids therethrough. Often, the stents are formed from a deformable metal and delivered to the desired intraluminal location by mounting the stent onto an expandable portion, e.g. a balloon, on the distal extremity of a delivery catheter. By advancing the catheter through the body lumen, the stent may be delivered to a desired position and expanded therein by expanding the expandable member, e.g. the balloon to an expanded configuration, seating it within the artery or other body lumen. Other implementations make use of a self-expanding stent formed from a suitable material such as pseudoelastic material that is delivered in a constricted condition and when released spontaneously expands to an enlarged configuration. In other embodiments, a stent made of shape memory alloy (e.g. NiTi alloy) may be inserted into the body lumen in a martensitic phase and transformed to an austenite phase which has an expanded memory when raised to a temperature above the transformation temperature, usually less than 45.degree. C.
Stents are often used in conjunction with an intravascular treatment for obstructive coronary artery disease. For example, ablation, atherectomy, balloon dilation, laser treatment or other procedures are among the method used to widen a stenotic region of a patient's vasculature. However, restenosis occurs in large percentage of percutaneous transluminal coronary angioplasty (PTCA) patients and rates can be even higher with other procedures. The prior art has employed a number of mechanical and pharmacological strategies to reduce the restenosis rate, but none have been particularly effective. Accordingly, stents have been proposed to maintain the patency of a treated vessel and prevent restenosis. Using stents, restenosis rates have fallen to less than 20%.
Restenosis is thought to be a natural healing reaction provoked by injury from the intravascular procedure. The healing process frequently causes thrombosis and may lead to intimal hyperplasia that occludes the vessel. Although helpful in reducing restenosis, stents do not represent a complete solution. The framework of the stent may still allow migration and proliferation of the smooth muscle cells, while the stent itself can be thrombogenic. To address these problems, stents have been covered with DACRON, PTFE and autologous vein and the stent surface has been seeded with endothelial cells or otherwise treated. Each of these solutions suffer from certain drawbacks, such as not being biocompatible, lacking sufficient mechanical strength, having a surface that is difficult to prepare, lack of ready availability and being thrombogenic. Antithrombotic drug regimens, in which anticoagulants and thrombolytic agents are administered during and after deployment of the stent, have also been employed to reduce the risk of thrombosis.
Thus, there remains a need for a stent capable of minimizing restenosis while having a consistency similar to the native artery, a non-thrombogenic surface and sufficient mechanical strength as well as being biocompatible and readily available. This invention satisfies these and other needs.